1. Field of the Invention
The present invention generally relates to an engine valve timing controller that controls a hydraulically driven variable valve timing mechanism. More particularly, the present invention relates to a technology for determining when operation of a hydraulically driven variable timing mechanism is permitted.
2. Background Information
Hydraulically driven valve timing mechanisms have been known for some time that allow for adjustment of the opening and closing timing (valve timing) of intake and exhaust valves. In such hydraulically driven valve timing mechanisms, the control response of the valve timing declines when the engine is cool and the viscosity of the oil is high. If the response delay causes the amount of valve overlap to become excessive, then misfiring can result.
In view of this issue, the valve timing controller presented in Japanese Laid-Open Patent Publication No. 10-176557 estimates the oil temperature, which has a high correlation to the responsiveness of the variable valve timing mechanism, based on the engine coolant temperature and reduces the overlap amount when the coolant temperature is low.
Meanwhile, the device presented in Japanese Laid-Open Patent Publication No. 7-233744 estimates the operation delay time of the hydraulically driven variable valve timing mechanism based on the coolant temperature and the intake air temperature. Based on the operation delay time, the device controls the ignition timing so as to absorb the torque step that accompanies switching of the valve timing.
In view of the above prior art, there exists a need for an improved engine valve timing controller. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
It has been discovered that the amount of change in the oil temperature with respect to the rise in the coolant temperature is not necessarily regular. Rather, it has been discovered that the amount of change in the oil temperature with respect to the rise in the coolant temperature varies greatly depending on the operating conditions.
When the amount of overlap is limited based on the coolant temperature in the manner previously described, the amount of overlap is limited up to a relatively high temperature region in order to reliably avoid misfiring in cases where the aforementioned variation occurs. Consequently, the region over which the amount of overlap can be expanded is narrowed.
Another problem is that the effect on driveability resulting from poor combustion (increased amount of residual gas in combustion chamber) accompanying the decline in responsiveness of the variable valve timing mechanism when the oil temperature is low cannot be sufficiently remedied by controlling the ignition timing alone.
The present invention was created in view of these problems. One object of the present invention is to provide an engine valve timing controller that can achieve a precise estimate of the oil temperature (which correlates with the responsiveness of the hydraulically driven variable valve timing mechanism). Therefore, the engine valve timing controller of the present invention can reliably avoid degradation of the driveability caused by a decline in responsiveness while also maintaining the largest possible region in which the amount of overlap can be expanded.
In accordance with one aspect of the present invention, an engine valve timing controller is provided for controlling a hydraulically driven variable valve timing mechanism. The engine valve timing controller basically comprises a coolant temperature, an intake air temperature detecting device and a control unit. The coolant temperature detecting device is arranged and configured to detect engine coolant temperature. The intake air temperature detecting device is arranged and configured to detect engine intake air temperature. The control unit is operatively coupled to the coolant temperature detecting device and operatively coupled to the intake air temperature detecting device to receive signals that are representative of the engine coolant temperature and the engine intake air temperature. The control unit is configured to control the variable valve timing mechanism by determining if both the engine coolant temperature and the engine air intake temperature at time of engine startup are greater than or equal to an operation assurance oil temperature of the variable valve timing mechanism, and then preventing operation of the variable valve timing mechanism until the engine coolant temperature at least reaches a first operation permission coolant temperature that is higher than the operation assurance oil temperature. The control unit is also configured to control the variable valve timing mechanism by determining if at least one of the engine coolant temperature and the engine intake temperature at time of engine startup is less than the operation assurance oil temperature, and then preventing operation of the variable valve timing mechanism until the engine coolant temperature at least reaches a second operation permission coolant temperature that is higher than the first operation permission coolant temperature.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.